The present invention relates to a hybrid compressor used mainly for vehicle air-conditioning systems. More specifically, the present invention pertains to a hybrid compressor driven by two drive sources including an engine and an electric motor and its control method.
Generally, a vehicle air-conditioning system includes a refrigeration circuit, which has a compressor and an external circuit connected to the compressor. When the compressor is driven by a vehicle engine, refrigerant circulates in the refrigeration circuit, which cools a vehicle compartment. Typically, the compressor is connected to a single drive source (engine) through an electromagnetic clutch. When the cooling capacity of the refrigeration circuit becomes excessive as the cooling load on the refrigeration circuit decreases, the electromagnetic clutch is turned off, or disengaged, which temporarily stops the operation of the compressor. When the engine is stopped, the compressor is not operated, and the vehicle compartment is not cooled.
Japanese Unexamined Utility Model Publication No. 6-87678 describes a hybrid compressor driven by an engine and an electric motor. The hybrid compressor is driven by the electric motor when the engine is not running, which allows the vehicle passenger compartment to be cooled while the engine is stopped.
The hybrid compressor includes a compression mechanism having a drive shaft, an electric motor having an output shaft connected to the drive shaft, and an electromagnetic clutch connected to the output shaft. The engine is connected to the output shaft through the electromagnetic clutch. When the clutch is engaged while the engine is running, the power of the engine is transmitted to the drive shaft through the output shaft, which operates the compression mechanism. At this time, the output shaft of the electric motor rotates with the drive shaft. The rotation of the output shaft generates electromotive force in the electric motor, and a battery is charged by electric power based on the electromotive force. When the output shaft and the drive shaft are disconnected from the engine by disengaging the clutch while the engine is stopped, the compression mechanism can be driven by the motor, which is powered by the battery.
The compression mechanism of the hybrid compressor is a swash plate type variable displacement compressor. In the compression mechanism, the displacement is controlled by adjusting the inclination angle of the swash plate in accordance with the cooling load on the refrigeration circuit, so that the refrigeration circuit has the appropriate cooling capacity. However, the engine and the electric motor, which are different kinds of drive sources, have different characteristics. Therefore, the operating conditions of the compression mechanism when driven by the engine are different from those when it is driven by the electric motor. This makes it difficult to smoothly shift the drive source of the compression mechanism from the engine to the electric motor.
The motor is powered by a battery, which stores a limited amount of power. Therefore, when the compression mechanism is driven by the electric motor, it is necessary to limit the power consumption by efficiently operating the electric motor in addition to maintaining an appropriate capacity.
Japanese Unexamined Utility Model Publication No. 6-87678 does not attempt to solve this problem.